Method and system for improving engine starting

ABSTRACT

An engine system and method for improving engine starting are disclosed. In one example, engine port throttles are adjusted to improve fuel vaporization of a fuel that includes alcohol. The system and method may improve engine starting and emissions.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/326,150, entitled “METHOD AND SYSTEM FOR IMPROVING ENGINESTARTING,” filed Dec. 14, 2011, now U.S. Pat. No. 8,899,212, the entirecontents of which are hereby incorporated by reference for all purposes.

BACKGROUND/SUMMARY

Starting an engine with a fuel that includes alcohol may be difficult atlower temperatures because it may be difficult to vaporize the alcoholand facilitate combustion. One way to improve vaporization of a fuelthat includes alcohol is to heat the fuel before the fuel is injected tothe engine. However, it may be difficult to provide enough heat to thefuel in a timely manner such that the fuel vaporizes when injected to acylinder. Specifically, it may be difficult to heat fuel to atemperature that allows vaporization of the fuel in the time betweencombustion events. Therefore, it may be desirable to provide a way tostart an engine with a fuel that includes alcohol that does not includeheating the fuel.

The inventors herein have recognized the above-mentioned limitations andhave developed a method of starting an engine, comprising: substantiallyclosing a port throttle of a cylinder; and injecting at least a portionof an amount of fuel to a cylinder during a cylinder cycle while theport throttle is substantially closed, the amount of fuel injected beingduring an interval that includes a middle position which issubstantially aligned with a predetermined vacuum level of the cylinder.

By closing a cylinder port throttle and creating vacuum in a cylinder,it may be possible to improve starting an engine with a fuel thatincludes alcohol. Specifically, a cylinder port throttle may be closedduring an intake stroke of a cylinder so that a vacuum level is providedin the cylinder that is greater than a vacuum in the cylinder when thecylinder is not port throttled. Further, fuel may be injected to thecylinder when vacuum within the cylinder is at a high level to improvefuel vaporization. In one example, fuel is injected at a timing that issubstantially symmetric about a predetermined vacuum level. Thepredetermined vacuum level may be a maximum vacuum level of the cylinderduring the cylinder's present cycle. In some examples, the maximumvacuum level during the cylinder cycle may be estimated from a positionof the engine. In this way, fuel injection timing is coordinated withcylinder port throttle position and piston position to improve fuelvaporization and engine starting.

The present description may provide several advantages. In particular,the approach may provide more robust engine starting at lower enginetemperatures. In addition, the method may reduce engine startingemissions by improving fuel vaporization and starting. For example,improved fuel vaporization may reduce engine misfires during startingand thereby reduce hydrocarbon emissions. Additionally, the approach maybe more cost effective as compared to other approaches since cylinderport throttles may be used for purposes other than engine starting. Forexample, port throttles may be useful for providing vacuum when intakemanifold pressure is high.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic depiction of an engine;

FIG. 2 shows a plot of example cylinder pressure;

FIGS. 3 and 4 show example simulated engine starting sequences;

FIG. 5 shows a detailed view of a simulated example of engine fueldelivery and port throttle operating during a cycle of a cylinder;

FIG. 6 shows a detailed view of a second simulated example of enginefuel delivery and port throttle operation during a cycle of a cylinder;

FIG. 7 shows a flowchart of an example method for starting an engine;

FIG. 8 shows an example simulated engine starting sequence; and

FIG. 9 shows a flowchart of a second example method for starting anengine.

DETAILED DESCRIPTION

The present description is related to controlling cylinder portthrottles of an engine as illustrated in FIG. 1. An example plot ofcylinder pressure is shown in FIG. 2 and it provides insight as tolocation of maximum vacuum within a cylinder during low engine speedconditions.

In one example, multiple cylinder port throttles are individuallyadjusted to provide improved fuel vaporization during engine starting.FIGS. 3 and 4 show signals of interest during engine starting. FIGS. 5and 6 provide detailed views of different fuel timings during enginestarting. Cylinder port throttles may be controlled according to themethod of FIG. 7 to provide the sequences illustrated in FIGS. 3-6. FIG.8 shows an alternative engine starting sequence for a system wherecylinder port throttles may be operated in unison. FIG. 9 is a flowchartof an alternative method for controlling cylinder port throttles.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53. Theposition of intake cam 51 may be determined by intake cam sensor 55. Theposition of exhaust cam 53 may be determined by exhaust cam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. If the fuel isport injected the port injector is positioned between intake valve 52and cylinder port throttle 83. Fuel injector 66 delivers liquid fuel inproportion to the pulse width of signal FPW from controller 12. Fuel isdelivered to fuel injector 66 by a fuel system (not shown) including afuel tank, fuel pump, and fuel rail (not shown). Fuel injector 66 issupplied operating current from driver 68 which responds to controller12. In addition, intake manifold 44 is shown communicating with optionalelectronic throttle 62 which adjusts a position of throttle plate 64 tocontrol air flow from engine air intake 42. Port throttle 83 controlsair flow into cylinder 30 via restricting or opening cylinder intakeport 81. In engines with a plurality of cylinders a plurality ofindividually controlled port throttles may be provided so that portthrottle of a first cylinder may be positioned differently from portthrottles of another cylinder. In other examples, each port throttle ofa cylinder bank may be mechanically coupled to other port throttles ofthe cylinder bank such that the port throttles of the cylinder bank movein unison.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing accelerator positionadjusted by foot 132; a measurement of engine manifold pressure (MAP)from pressure sensor 122 coupled to intake manifold 44; an engineposition sensor from a Hall effect sensor 118 sensing crankshaft 40position; a measurement of air mass entering the engine from sensor 120(e.g., a hot wire air flow meter); and a measurement of throttleposition from sensor 58. Barometric pressure may also be sensed (sensornot shown) for processing by controller 12. In a preferred aspect of thepresent description, engine position sensor 118 produces a predeterminednumber of equally spaced pulses every revolution of the crankshaft fromwhich engine speed (RPM) can be determined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof. Further, in some embodiments, other engine configurations maybe employed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is described merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

Thus, the system of FIG. 1 provides for an engine, comprising: an engineair intake throttle located along an engine air intake passage; a firstengine cylinder port throttle located along the engine air intakepassage downstream of the engine air intake throttle; a first fuelinjector located downstream of the first engine cylinder port throttle;a cylinder receiving a fuel via the first fuel injector and air via thefirst engine cylinder port throttle; and a controller includinginstructions for injecting substantially a same amount of fuel beforeand after a predetermined vacuum level of the cylinder is reached duringa cycle of the cylinder, and including additional instructions foropening the first engine cylinder port throttle after the first fuelinjector begins to inject fuel during the cycle of the cylinder. In thisway, fuel may be injected at times when fuel vaporization may beincreased.

The system also includes where the first fuel injector is a direct fuelinjector, and further comprising a second engine cylinder port throttle,and further comprising additional instructions for adjusting the secondengine cylinder port throttle independent of the first engine cylinderport throttle. The system further comprises additional instructions forsubstantially fully opening the first engine cylinder port throttleafter the engine reaches a predetermined engine speed. In some examples,the system includes where the same amount of fuel injected to thecylinder before and after the predetermined vacuum level is reached isinjected in two separate pulses. The system further comprises additioninstructions for substantially closing the first engine cylinder portthrottle after an intake valve of the cylinder is closed during thecycle of the cylinder. The system further includes where the first fuelinjector is a port fuel injector, and further comprising additionalinstructions to inject fuel to the cylinder via the port fuel injectorwhile an intake valve of the cylinder is open.

Referring now to FIG. 2, an example plot of cylinder pressure for anengine operating at 750 RPM is shown. The X axis indicates cylindervolume and cylinder volume increases from left to right. The Y axisindicates cylinder pressure and pressure increases from the bottom tothe top of the plot. Cylinder pressure is represented by curve 200.

Pressure in the cylinder follows the trajectory indicated by directionalarrows 210, 212, 214, and 216 for respective intake, compression,expansion, and exhaust strokes. The cylinder volume increases as thepiston moves toward bottom dead center intake stroke in the direction ofarrow 210. Cylinder pressure reaches a minimum level indicated byhorizontal line 202 shortly before the piston reaches bottom dead centerintake stroke at 204. Fuel may be injected to the cylinder or a cylinderintake port such that the middle of the fuel injection interval issubstantially centered on the minimum cylinder pressure indicated at206. The cylinder pressure begins to increase and follow the trajectoryindicated by arrow 212 after the piston travels past bottom dead centerand enters the compression stroke.

Notice that the trajectory of cylinder pressure curve 200 has ashallower slope to the left of marker 206 and cylinder pressure risesmore quickly to the right of marker 206. Therefore, in some examples, aportion of the fuel injection duration may be biased advanced (e.g., tothe left of marker 206, during the intake stroke) when centering thefuel injection interval over the minimum cylinder pressure would place aportion of the injection interval in a higher pressure region of thecylinder pressure as compared to the injection interval on the otherside of the middle point of the injection interval. For example, 60% ofa fuel injection pulse during a cylinder cycle may be injected at a timeto the left of marker 206 while the remaining 40% of the fuel injectionpulse may be placed to the right of marker 206. In this way, the fuelinjection pulse may be located such that the fuel injected during theinjection interval is exposed to the lowest pressure in the cylinderover the duration of the injection interval.

The middle portion of a fuel injection interval may be substantiallypositioned at bottom dead center intake stroke when the middle portionof the fuel injector interval is within the period where the cylindervolume is within 20% of the maximum cylinder volume during the intakeand/or compression stroke of the cylinder. In other examples, the middleportion of a fuel injection interval may be substantially positioned atbottom dead center intake stroke when the middle portion of the fuelinjector interval is within the period where the cylinder volume iswithin 10% of the maximum cylinder volume during the intake and/orcompression stroke of the cylinder. For example, the middle portion ofthe fuel injection interval may be positioned at marker 206 or wherecylinder volume is at 500 and still be considered substantiallypositioned at bottom dead center intake stroke.

Referring now to FIG. 3, an example engine starting sequence isillustrated. The sequence may be provided by controller 12 executinginstructions of the method described in FIG. 7 within the system shownin FIG. 1. The sequence is illustrative of an engine including an airinlet throttle and cylinder port throttles.

The first plot from the top of FIG. 3 represents trajectories of pistonsin cylinders 1 and 4 of a four cylinder, four stroke engine, having afiring order of 1-3-4-2. Line 302 represents the position of the pistonof cylinder number one while line 304 represents the position of thepiston of cylinder number three. Each of the pistons is at top deadcenter when the trajectory is at the top of the sinusoid. Each of thepistons is at bottom dead center at the bottom of the sinusoid. Dots 306represent timing of intake valve closing for each cylinder relative tothe piston trajectory. Time begins at the left side of the plot andincreases to the right side of the plot.

The second plot from the top of FIG. 3 represents cylinder intake portpressure for cylinder ports of cylinders number one and three. The solidline 308 represents cylinder port pressure for cylinder number one. Thedotted line 309 represents cylinder port pressure for cylinder numberthree. The Y axis represents cylinder pressure and cylinder pressureincreases in the direction of the Y axis arrow. The X axis representstime and time increases from the left side to right side of the plot.Horizontal line 330 represents atmospheric pressure. Thus, when cylinderintake port pressure is below horizontal line 330 vacuum exists in thecylinder port.

The third plot from the top of FIG. 3 represents fuel injection timingfor cylinders one and three of the engine. Fuel injection for cylinderone is represented by solid line 310. Fuel injection for cylinder threeis represented by dotted line 312. The Y axis represents when fuel isbeing injected. A fuel injection above the X axis indicates that fuel isinjected at the illustrated time. The X axis represents time and timebegins at the left side of the plot and increases to the right side ofthe plot. The numbers above the fuel pulses indicate into which cylinderthe fuel is injected. Thus, the numbering follows the engine order ofcombustion.

The fourth plot from the top of FIG. 3 represents air inlet throttleposition versus time. The Y axis represents air inlet throttle openingamount and the throttle opening amount increases in the direction of theY axis arrow. The X axis represents time and time increases from theleft side of the plot to the right side of the plot.

The fifth plot from the top of FIG. 3 represents position of a firstport throttle that can regulate air flow to cylinder number one versustime. The Y axis represents port throttle opening amount and the portthrottle opening amount increases in the direction of the Y axis arrow.The X axis represents time and time increases from the left side of theplot to the right side of the figure.

The sixth plot from the top of FIG. 3 represents position of a thirdport throttle that can regulate air flow to cylinder number three versustime. The Y axis represents port throttle opening amount and the portthrottle opening amount increases in the direction of the Y axis arrow.The X axis represents time and time increases from the left side of theplot to the right side of the plot.

The seventh plot from the top of FIG. 3 represents a desired cylinderindicated mean effective pressure (IMEP) during a combustion processduring a cylinder cycle. IMEP can be increased by increasing the amountof air and fuel inducted into the cylinder. The Y axis represents IMEPand IMEP increases in the direction of the Y axis arrow. The X axisrepresents time and time increases from the left side of the plot to theright side of the plot.

The eighth plot from the top of FIG. 2 represents engine speed versustime. The Y axis represents engine speed and engine speed increases inthe direction of the Y axis arrow. The X axis represents time and timeincreases from the left side of the plot to the right side of the plot.

Vertical markers T₀-T₁₈ represent times of interest in the sequence. Thesequence begins at time T₀and proceeds in the direction of T₁₈.

At time T₀, the engine is stopped and fuel is not injected to theengine. The air inlet throttle is set to a substantially closed positionas are the first and third port cylinder throttles. The desired cylinderIMEP value is commanded relatively high so that the engine may quicklyaccelerate from cranking speed to idle speed during the engine start.The piston for cylinder number one is stopped just prior to top deadcenter (TDC) exhaust stroke. The piston for cylinder number three isstopped just prior to bottom dead center (BDC) power stroke.

Between time T₀ and time T₁, the engine is cranked via a starter and thepistons start to move in the cylinders. Engine speed increases to crankspeed (e.g., 250 RPM). As the engine rotates, the engine controller 12judges how much fuel to inject to cylinders as well as how much air toallow in the cylinders. The engine controller also determines when tobegin and end injection of fuel as well as spark timing. In someexamples, engine position may be determined from camshaft and crankshaftposition sensor during cranking In other examples, engine position maybe stored in memory at the time the engine stops.

At time T₁, the piston for cylinder number one (e.g., see trajectory ofline 302) approaches BDC intake stroke. The first injection of fuelsince engine stop occurs at time T₁ where fuel is injected to cylindernumber one. Fuel may be directly injected to the cylinder number one orinto an intake port of cylinder number one. Fuel injection continuesuntil time T₂. Thus, the fuel injection interval for the first injectionof fuel into cylinder number one since engine stop is the time betweentime T₁ and T₂. Further, the amount of fuel injected is during aninterval, and the interval includes a middle position which issubstantially aligned with maximum cylinder port vacuum (minimumcylinder pressure) during a cylinder cycle or with bottom dead centerintake stroke of the cylinder. In some examples, the fuel injectioninterval may be measured in crankshaft degrees. Notice that the fuelinjection interval for cylinder number one is centered about the minimumpressure in cylinder number one intake port. For example, the sameamount of fuel is injected to the cylinder before the pistonsubstantially reaches minimum cylinder port pressure as after thecylinder port pressure begins to increase. In some examples, theinjection time may be centered on bottom dead center intake stroke ofthe cylinder. In this example, fuel is injected in a single pulse width;however, in other examples fuel may be delivered to a cylinder in two ormore separate pulses.

The first port throttle is held closed from time T₀ to time T₂ so thatvacuum develops in cylinder number one as the volume of the cylinderincreases. The vacuum in cylinder number one reaches a near maximumvalue when the piston of cylinder number one approaches BDC. Thus,injecting fuel to the cylinder where maximum vacuum occurs may improvevaporization of fuels such as alcohol. The first port throttle begins toopen at time T₂. However, in other examples the first port throttle maybegin before end of fuel injection. Opening the first port throttleallows air to enter the cylinder at a higher flow rate so that a desiredamount of air may enter the cylinder. The desired amount of air may bebased in the desired IMEP. The timing that the first port throttle isopened, and the amount the first port throttle is opened, controls theamount of air that enters the cylinder. Said another way, opening theport throttle after the injection but before intake valve closing (IVC),governs the air charge. Air charge is set by cylinder pressure at IVC.For many tens of degrees after IVC, the port throttle position has noinfluence over either fuel vaporization or air charge control. Thislessens the engine synchronous port throttle control requirements. Theintake valve closing time of cylinder number one at T₃, as indicated bythe dot, determines when air flow into the cylinder stops. Thus, airflow into the cylinder is increased by opening the first port throttle.On the other hand, air flow into cylinder number one is stopped byclosing the intake valve of cylinder number one. In this way, airflowing into the cylinder may be controlled by the first port throttleopening time and the intake valve closing time of cylinder number one.

It should be noted that at lower engine speeds, such as during crankingand at least a portion of engine run-up to idle speed, cylinder portthrottles may be opened according to crankshaft position since enginespeed is low and time between cylinder intake events is relatively long.Closing timing of the cylinder port throttles is less important becauseintake valve closing timing determines when air flow into cylindersstops. In this way, the dynamic demands of moving the cylinder portthrottles may be reduced, yet the cylinder port throttles may meter airflow into engine cylinders. Further, the cylinder port throttles areangularly synchronized with the engine crankshaft position when enginespeed is less than a threshold speed. For example, the cylinder portthrottles may be opened at predetermined crankshaft timings duringcranking and run-up.

Thus, fuel is injected to cylinder number one when vacuum in thecylinder port is high (e.g., when pressure in the port is low) during acylinder cycle, and air is allowed to flow into the cylinder after thefuel is vaporized to provide a cylinder air amount that matches the fuelamount at a desired ratio (e.g., an air-fuel ratio of 10:1). The firstport throttle is closed as cylinder number one proceeds through itscylinder cycle and before another air charge is inducted into cylindernumber one.

The third port throttle remains closed during the time period between T₁and T₃. The air inlet throttle is also shown in a closed position andthe desired cylinder IMEP stays at a high level so that the engine canbe rapidly accelerated from cranking speed to idle speed.

At time T₄, the piston of cylinder number three approaches BDC and fuelinjection to cylinder number three begins. Fuel injection into cylindernumber three continues until time T₅. It can be noticed that the fuelsupplied to cylinder number three is also distributed symmetricallyabout the time cylinder number three port pressure is at a minimumduring the cylinder cycle. The third port throttle begins to open afterfuel injection to cylinder number three ceases at time T₅. However, thethird port throttle may begin to open earlier, but fuel vaporization maybe reduced of the cylinder port throttle is opened during fuelinjection. The third port throttle is opened less when the intake valveof cylinder number three closes at time T₆ as compared to the amount thefirst port throttle is opened when the intake valve of cylinder numberone closes at time T₃. Consequently, the amount of air inducted tocylinder number three during its first combustion cycle is less thanthat of cylinder number one during its first combustion cycle. Theamount of air and fuel allowed into cylinder number three is reducedbased on the reduced desired IMEP. The IMEP is reduced so that enginespeed does not overshoot the desired engine speed by a large amount. Thethird port throttle is closed before a subsequent combustion cyclebegins.

Between time T₆ and time T₇, the engine accelerates and the enginerotates through additional cylinder cycles. As engine speed increases,the desired cylinder IMEP decreases so that engine speed does notovershoot the desired engine speed by more than a desired amount. Theair inlet throttle also remains closed to that air in the engine intakemanifold decreases.

At time T₇, the piston of cylinder number one is again approaching BDCof an intake stroke so start of fuel injection begins for the presentcycle of cylinder number one. The fuel injection is again substantiallycentered about minimum cylinder port pressure (maximum cylinder portvacuum) during a cylinder cycle, and cylinder minimum port pressurecorrelates to cylinder minimum pressure. So, fuel injection canalternatively be centered about minimum cylinder pressure in this cycleas well as other cylinder cycles. Fuel injection to cylinder number oneceases at time T₈. Similar to during the first combustion cycle ofcylinder number one, the first cylinder port throttle begins to openafter fuel injection is ceased. The intake valve of cylinder number onecloses at time T₉ and air flow into cylinder number one stops. As theengine accelerates the amount of time between cylinder strokesdecreases. However, the amount of fuel injected to the cylindersdecreases with decreasing desired cylinder IMEP. Therefore, the shortertime between cylinder cycles is at least somewhat counteracted by theshorter amount of time it takes to inject smaller amounts of fuel intothe cylinders. Additionally, the first cylinder port throttle is openedless as compared to during the previous combustion cycle of cylindernumber one to reduce cylinder IMEP and to achieve a desired cylinderair-fuel mixture.

Between times T₁₀-T₁₂, the piston of cylinder number three is againapproaching BDC of an intake stroke so fuel is injected symmetricallyabout minimum cylinder port pressure intake stroke of cylinder numberthree. Additionally, the third cylinder port throttle position isadjusted to further reduce IMEP as the desired IMEP continues todecrease.

Between times T₁₃-T₁₈, pistons of cylinder numbers one and three againapproach respective BDC locations of intake strokes so fuel is injectedsymmetrically about minimum cylinder port pressure during intake strokeof the cylinder. The first and third port throttles are also adjusted toreduce the IMEP of cylinders one and three. However, instead of closingagain, the first and third cylinder port throttles are fully opened andair flows into the cylinders being regulated via the air inlet throttle.The air inlet throttle opens to allow air flow into the engine cylindersat a level that provides torque to achieve a desired engine speed.Engine speed continues to increase and eventually levels out to adesired engine speed.

In this way, fuel may be injected to engine cylinders during enginestarting to promote fuel vaporization. Additionally, port throttles canbe adjusted as shown to promote fuel vaporization and control cylinderair amount so that a desired IMEP may be achieved. In some examples,fuel injection timing may be adjusted to provide up to 25% more fuel onone side of minimum cylinder pressure or BDC intake stroke as comparedto the other side of minimum cylinder pressure or BDC intake stroke.

For example, where the total amount of fuel injected to a cylinderduring a cycle of the cylinder is 3.3×10⁻² grams, 2.48×10⁻² grams offuel may be injected advanced of BDC intake stroke while 0.82×10⁻² gramsof fuel may be injected retarded of BDC intake stroke during a cylindercycle. Conversely, 2.48×10⁻² grams of fuel may be injected retarded ofBDC intake stroke while 0.82×10⁻² grams of fuel may be injected advancedof BDC intake stroke during a cylinder cycle. Such an adjustment canallow for conditions where highest cylinder vacuum about BDC intakestroke may vary from BDC intake stroke.

FIG. 3 also shows that fuel is injected about minimum cylinder portpressure or BDC intake stroke for each engine cylinder for threecombustion events since engine stop. However, fuel may be injected aboutminimum cylinder port pressure or BDC for a predetermined number ofcombustion events since engine stop that varies with engine operatingconditions. Alternatively, fuel may be injected about minimum cylinderport pressure or BDC for the respective intake strokes of cylindersnumber one through four for a predetermined amount of time since enginestop. It should also be noted that fuel may be injected about minimumcylinder port pressure in a similar manner as injecting fuel aboutminimum cylinder port pressure as is shown in FIG. 3.

Referring now to FIG. 4, signals of interest during an engine start areshown. The signals of FIG. 4 are similar to those of FIG. 3. Further,similar signals are numbered similarly with the exception of the leadingnumber of the identifier which follows the Fig. number. For example,signal 402 of FIG. 4 represents a position of a piston of cylindernumber one and it follows the same trajectory of signal 302 in FIG. 3.Additionally, the time of vertical timing markers T₀ to T₁₈ areidentical to similar timing events in FIG. 3. Therefore, for the sake ofbrevity, descriptions of common features are omitted and differencesbetween the sequence of FIG. 3 and the sequence of FIG. 4 are described.

At times T₁₅ and T₁₈, the first and third port throttles are held openat a middle position away from the substantially closed position.Adjusting the port throttles to a middle position allows the portthrottles to regulate air flow into the respective cylinders during theentire time the intake valves of the cylinders are open. For example, ifthe intake valve of cylinder number one is open from TDC intake strokeof cylinder number one to twenty degrees after BDC intake stroke ofcylinder number one, the first port throttle regulates air to flow thefirst cylinder from TDC intake stroke of cylinder number one to twentydegrees after BDC intake stroke of cylinder number one. In this way,cylinder air flow may be regulated by the individual port throttles sothat the air inlet throttle may be removed from the system.

Referring now to FIG. 5, a detailed view of a simulated example ofengine fuel delivery to a cylinder and port throttle operation during acycle of a cylinder are shown. The method of FIG. 7 executed bycontroller 12 in the system of FIG. 1 may provide the illustratedsequence.

The first plot from the top of FIG. 5 represents a trajectory of apiston in cylinder number one of a four cylinder, four stroke engineversus time. The piston is at top dead center when the trajectory is atthe top of the sinusoid. The piston is at bottom dead center at thebottom of the sinusoid. Time begins at the left side of the plot andincreases to the right side of the plot.

The second plot from the top of FIG. 5 represents fuel injection timingcylinder number one. A first fuel injection timing 502, a second fuelinjection timing 504, and an optional third fuel injection 510 are shownversus time. The Y axis represents when fuel is being injected. A fuelinjection above the X axis indicates that fuel is injected at theillustrated time. The X axis represents time and time begins at the leftside of the plot and increases to the right side of the plot.

The third plot from the top of FIG. 5 represents position of a firstport throttle that can regulate air flow to cylinder number one versustime. The Y axis represents port throttle opening amount and the portthrottle opening amount increases in the direction of the Y axis arrow.The X axis represents time and time increases from the left side of thefigure to the right side of the figure.

The fourth plot from the top of FIG. 5 represents cylinder number oneport pressure versus time. The Y axis represents cylinder port pressureand cylinder port pressure increases in the direction of the Y axisarrow. The X axis represents time and time increases from the left sideof the figure to the right side of the figure.

Pressure in the cylinder port decreases after the intake valve opens andthe piston of the cylinder passes TDC intake stroke. The cylinder portpressure reaches minimum level at substantially BDC intake stroke.Injector pulse 504 begins injecting fuel before cylinder number onereaches minimum cylinder pressure near BDC intake stroke. Injector pulse504 ends injecting fuel after cylinder number one reaches minimumcylinder pressure during the cylinder cycle after BDC intake stroke.Further, injector pulse 504 is positioned symmetrically about minimumcylinder pressure during the cylinder cycle so that the entire fuelpulse width experiences the lowest cylinder pressure during a cycle ofthe cylinder. In this way, as much injected fuel as possible may beexposed to a highest vacuum in a cylinder during a cycle of thecylinder. As such, fuel vaporization in the cylinder may be improved ascompared to when fuel is simply injected during intake valve openingtime.

On the other hand, fuel injection pulse 502 is shown starting to injectfuel advanced of when fuel injection pulse width 504 begins to injectfuel to the cylinder. In some examples, the timing of fuel injectionpulse 502 may be advanced to the timing of fuel injection pulse 504 toaccount for the shallow slope of curve 200 during the intake stroke ofthe cylinder cycle as shown in FIG. 2. Further, fuel injection timingmay be advanced as an engine warms and as fuel vaporization via vacuummay be less necessary. Advancing start of fuel injection timing to thatof pulse 504 may improve cylinder air-fuel mixing. Thus, in someexamples, fuel injection to a cylinder may begin at the timing of 504and advance to the timing of 502.

FIG. 5 also shows that the first port throttle may begin to open shortlybefore fuel injection to cylinder number one ceases. Such operation ofthe first port throttle may be provided when the port throttle cannotopen enough between the end of fuel injection and closing of the intakevalve of cylinder number one to provide the cylinder a desired cylinderair amount. The pressure in the cylinder port increases as the firstport throttle is opened. Opening the first port throttle allows pressurein the cylinder port to approach intake manifold pressure. In this way,most of the air entering cylinder number one occurs between the openingtime of the first port throttle and the closing time of the intake valveof cylinder number one. Thus, the first port throttle and the cylinderintake valve control air flow to cylinder number one.

The second fuel pulse 510 may be injected late in the compression strokeof the cylinder to take advantage of cylinder heating throughcompression work. When fuel is injected late during the compressionstroke (e.g., within 45 crankshaft degrees of TDC compression stroke)heat of compression may further assist fuel vaporization and mixing.Thus, a first injection may leverage vacuum in the cylinder while asecond injection leverages heat in the cylinder. Consequently, fuelvaporization may be enhanced in two separate injection modes (e.g.,vacuum enhanced vaporization and heat enhanced vaporization) during acylinder cycle.

Referring now to FIG. 6, the signals of FIG. 6 are identical to thecylinders of FIG. 5 with the exception of fuel pulses 602 and 604.Therefore, the description of redundant elements is omitted anddifferences between FIGS. 5 and 6 are described.

In this example, a total amount of fuel injected to cylinder number oneis comprised of two fuel pulse widths 602 and 604. Additionally, anoptional third fuel pulse 610 may be provided to utilize heat ofcompression. In some examples, fuel pulse width 602 may be advancedwhile fuel pulse 604 may remain near minimum cylinder pressure or nearBDC intake stroke as the engine begins to warm after starting. Thus, thetiming of when the two fuel pulse widths are injected may initially besymmetric about minimum cylinder pressure (e.g., maximum cylindervacuum) during a cylinder cycle or BDC intake stroke of a cylinder, andas the engine warms, the timing of the two fuel pulses may be comeasymmetric. The third fuel pulse 610 may utilize compression heat tovaporize additional fuel injected to the cylinder.

Referring now to FIG. 7, a flowchart of an example method for startingan engine is shown. The method of FIG. 7 may be included in instructionsof controller 12 shown in the system of FIG. 1.

At 702, method 700 determines engine operating conditions. Engineoperating conditions may include but are not limited to engine speed,engine temperature, barometric pressure, engine position, time sinceengine stop, and combustion events since engine stop. Method 700proceeds to 704 after engine operating conditions are determined.

At 704, method 700 determines the type of fuel to be injected to theengine. In one example, the fuel type may be determined via a fuel typesensor. In other examples, the fuel type may be inferred from an oxygensensor and stored in memory. For example, the method described in U.S.Pat. No. 6,644,097 which is hereby fully incorporated by reference maybe the basis for determining fuel type. Once the fuel type isdetermined, it may be stored in controller memory and stored forsubsequent retrieval.

At 706, method 700 determines an amount of fuel to inject to the engineand amounts of air to induct into engine cylinders. In one example, theamount of fuel injected to the engine and cylinder air amounts may bebased on an engine torque request and the fuel type at time of enginestart. For example, desired engine torque or cylinder pressure (e.g.,IMEP) at engine starting may empirically determined and stored inmemory. Upon an engine start request, the engine torque amount orcylinder pressure may be retrieved from memory. The engine torque orcylinder pressure may be converted to a cylinder air amount and fuelamount according to the method described in U.S. Pat. No. 7,321,821which is hereby incorporated by reference for all intents and purposes.Where different fuels may be combusted by the engine, a multiplicationfactor may be used to adjust the amount of fuel injected so that thedesired engine torque is provided by different fuel types. Method 700proceeds to 708 after fuel amount and cylinder air amounts aredetermined.

At 708, method 700 determines an amount of advance to adjust fuelinjection start of injection timing. In other words, method 700determines how much earlier in time or crankshaft position to adjustfuel injector start of injection from base fuel injection timing. In oneexample, fuel injector advance is empirically determined and stored intables or functions that may be indexed via engine temperature andnumber of combustion event from engine stop time. Thus, as the enginewarms the fuel injection timing may be advanced.

In some examples, the amount of time fuel injection is advanced relativeto crankshaft position may be based on fuel type. For example, ifgasoline is injected to a cylinder, the fuel injection start ofinjection time may be advance further than a fuel that contains alcohol.As the alcohol content of the fuel increases, the start of injectiontime moves closer to base fuel injection timing. In one example, basestart if injection timing is based on 100% ethanol fuel. Method 700proceeds to 710 after fuel injector timing advance is determined.

At 710, method 700 closes the cylinder port throttles. The cylinder portthrottles may be independently controlled such that some cylinder portthrottles may be partially open while others are substantially closed.Closing the cylinder port throttle allows additional vacuum to begenerated in engine cylinders as compared to vacuum in the engine intakemanifold. Method 700 proceeds to 712 after the engine port throttles areclosed.

At 712, method 700 judges whether or not the engine is cranking orrotating via a starter or a motor. In one example, method 700 judgesthat the engine is cranking when engine speed is greater than athreshold speed. Method 700 proceeds to 714 if it is judged that theengine is cranking Otherwise, method 700 returns to 712.

At 714, the fuel injection timing is determined. In one example, theamount of time it takes to inject a desired amount of fuel to a cylinderis determined via a transfer function of a fuel injector. For example, adesired fuel amount is used to index a table or function that describesinjector operation. The table or function outputs a time to open theinjector to deliver the desired amount of fuel at the present fuelpressure (e.g., 40 ms). The time to inject the fuel is divided by two,and fuel injection to a cylinder commences 20 ms before the cylinderreaches minimum pressure during a cycle of the cylinder or when thepiston is substantially at BDC so that the entire pulse width of 40 msis symmetrically distributed in time and relative to minimum cylinderpressure or crankshaft position about BDC intake stroke of the cylinderreceiving the fuel. The start of injection timing may be converted to acrankshaft angle relative to minimum cylinder pressure or BDC intakestroke of the cylinder receiving the fuel since start of injection timemay be correlated to an engine position (e.g., BDC intake stroke of acylinder). For example, for an engine that has a cranking speed of 250RPM, start of fuel injection may begin 30 crankshaft degrees before BDCintake stroke of the cylinder receiving fuel when the total fuelinjection time is 40 ms. Since it takes the engine 20 ms to rotate 30crankshaft degrees (e.g., 30 deg=20 ms·250 RPM·360 deg/rev·1s/1000 ms·1min/60 sec), the fuel is delivered substantially about BDC intake strokeof the cylinder. If fuel injection time is to be advanced from basetiming, the advance amount determined at 708 is added to the start offuel injection timing to further advance fuel injection timing. In thisway, fuel injector timing may be determined. Method 700 proceeds to 716after fuel injection timing is determined.

At 716, method 700 injects fuel to the engine at the prescribed timingvia opening a fuel injector. The fuel injector may be opened at acrankshaft angle as determined at 714 for the amount of time determinedat 706. Optionally, an additional fuel injection may commence late inthe compression stroke during a cylinder cycle to utilize compressionheating. Thus, a portion of injected fuel may be vaporized via vacuumwhile the remainder of injected fuel may be vaporized utilizingcompression heat. Method 700 proceeds to 718 after fuel injection timingis output.

At 718, method 700 opens a cylinder port throttle to provide a desiredair amount to the cylinder as described at 706. In one example, the flowair flow through the cylinder port throttle may be described by afunction or table that relates pressure drop across the cylinder portthrottle and port throttle position to air flow through the portthrottle. Further, the amount of time to fully open the cylinder portthrottle may be empirically determined and stored in memory. Based onthe maximum cylinder port throttle opening rate and the cylinder portthrottle flow description, the flow through the throttle is integratedsuch that an amount of time it takes to flow the desired air amountthrough the port throttle is determined. The cylinder port throttle isopened the determined amount of time before the intake valve of thecylinder is closed. In some examples, an offset to account for valvelift and engine speed effects may be added to the time determined toflow the desired air amount through the cylinder port throttle. Thecylinder port throttle is opened, for the cylinder receiving the fuel,the amount of time it takes to flow the desired cylinder air amountthrough the port throttle before the intake valve closes. For example,if it is determined that it takes 25 ms to flow a desired air amountthrough a cylinder port throttle, the cylinder port throttle is opened25 ms before the intake valve closes. Method 700 proceeds to 720 afterthe cylinder port throttle is scheduled and output.

At 720, method 700 judges whether or not the engine has exited crank andrun-up. In one example, it may be judged that the engine has exitedcrank and run-up when engine speed exceeds a threshold engine speed. Ifthe engine has exited crank and run-up method 700 proceeds to exit. Ifthe engine includes an air inlet throttle, the cylinder port throttlesmay transition to a fully open position upon exiting method 700. If theengine does not include an air inlet throttle, the cylinder portthrottles may transition to a partially open position such that theengine operates at a desired engine idle speed.

Alternatively, method 700 may exit after a predetermined number ofcombustion events have occurred or if some other engine condition suchas a desired engine temperature or desired engine speed is reached. Inthis way, an engine controller may inject fuel to a cylindersymmetrically about maximum cylinder vacuum (minimum cylinder pressure)or BDC intake stroke of the cylinder and then transition to a differentfuel injection mode.

At 722, method 700 substantially closes a cylinder port throttle afterthe desired amount of air has passed through the cylinder port throttleand into the cylinder. Further, the cylinder air amount and cylinderfuel amount determined at 706 may be revised based on present engineoperating conditions (e.g., number of combustion events since enginestop, engine temperature, time since engine stop) as described at 706.Method 700 returns to 714 after the cylinder port throttle is closed.

In this way, method 700 may operate fuel injectors and cylinder portthrottles as illustrated in FIGS. 3-6. Method 700 may execute for eachcylinder of an engine so that all cylinder port throttles and fuelinjectors may be controlled to provide desired cylinder fuel and airamounts.

Referring now to FIG. 8, signals of interest during an engine start areshown. The signals of FIG. 8 are similar to those of FIGS. 3 and 4.Further, similar signals are numbered similarly with the exception ofthe leading number of the identifier which follows the Fig. number. Forexample, signal 802 of FIG. 8 represents a position of a piston ofcylinder number one and it follows the same trajectory of signal 302 inFIG. 3. Additionally, the time of vertical timing markers T₀ to T₁₈ areidentical to similar timing events in FIG. 3. Therefore, for the sake ofbrevity, descriptions of common features are omitted and differencesbetween the sequence of FIG. 3 and the sequence of FIG. 8 are described.

In the example sequence of FIG. 8, cylinder port throttles aremechanically coupled together so that when cylinder number one portthrottle is moved, cylinder number three port throttle also moves. Theport throttles are also at similar positions. For example, when cylindernumber three port throttle is closed, cylinder number one port throttleis closed.

Cylinder port throttles for cylinders number one and three aresubstantially closed at time T₀ and open after time T₁₈. The cylinderport throttles may be opened together based on when intake manifoldpressure is reduced to a predetermined pressure, after a predeterminednumber of induction events or combustion events from engine stop, orafter engine speed reaches a predetermined threshold speed.

Fuel is injected to each cylinder such that the fuel pulse issubstantially centered about minimum cylinder port pressure (e.g.,maximum cylinder port vacuum) or BDC intake stroke of the cylinder.Alternatively, the fuel injection interval may be substantially centeredor slightly advance from maximum cylinder vacuum or within the time whencylinder volume is within 20% of maximum cylinder volume during thecylinder intake stroke.

In this way, an engine having port throttles that are mechanicallycoupled together may be operated during an engine start. Operating aplurality of port throttles together via a single actuator may reducesystem cost.

Since the port throttles only control air pressure at the injection andair charge during the intake stroke and the compression stroke untilIVC, port throttles for multiple cylinders can share a shaft (and thusposition) without sacrificing the feature originally described withindependent port throttles between cylinders. This is because for nearly3/4 of all engine positions, the port throttle position is “don't care”,meaning, a single port throttle's position is not controlling air andfuel charging during that angular portion.

Referring now to FIG. 9, a flowchart of a method for starting an engineis shown. The method of FIG. 9 is applicable to engine systems thatinclude port throttle that are mechanically coupled together. Theoperations of FIG. 9 are similar to those of FIG. 7. Further, similaroperations are numbered and labeled similarly with the exception of theleading number of the identifier which follows the FIG. number. Forexample, engine operating conditions are determined at 902 of FIG. 9while engine operating conditions are determined at 702 of FIG. 7.Therefore, for the sake of brevity, descriptions of common operationsare omitted and differences between operations of FIG. 7 and the methodof FIG. 9 are described.

At 910, method 900 adjusts the position of cylinder port throttles of acylinder bank to a position for cranking The port throttle positionduring cranking may be empirically determined and adjusted forbarometric pressure. For example, a function that describes portthrottle position based on barometric pressure may be indexed viabarometric pressure to determine a desired cylinder port throttleposition. The desired cylinder port throttle may be commanded beforeengine cranking begins. Method 900 proceeds to 912 once the position ofcylinder port throttles is set.

At 918, the position of cylinder port throttles may be adjusted. In oneexample, the position of port throttles may be adjusted during enginecranking based on the number of cylinder air induction events or numberof combustion events since engine stop. For example, after a firstinduction event the cylinder port throttle may be opened further sincepressure in the intake manifold may be reduced as air is transferredfrom the intake manifold to an engine cylinder. In this way, uniformcylinder air amounts may be provided for several cylinder air inductionevents if desired. In other examples, the cylinder port throttlepositions may be held at a constant state during engine cranking

At 920, method 900 judges whether or not to exit crank and run-up. Inone example, method 900 may exit crank and run-up mode when engine speedexceeds a threshold engine speed. In another example, method 900 mayexit crank and run-up mode when intake manifold pressure is reduced to alevel less than a threshold pressure. In still another example, method900 may exit crank and run-up mode after a predetermined number ofcylinder combustion events. If method 900 exits crank and run-up, method900 proceeds to 922. Otherwise, method 900 returns to 914.

At 922, method 900 opens cylinder port throttle to a fully openposition. By opening the cylinder port throttles to a fully openposition, method 900 allows air flowing into engine cylinders to beregulated by the air inlet throttle and cylinder intake valves. Method900 proceeds to exit after the cylinder port throttles are opened.

Thus, the methods of FIGS. 7 and 9 provides for a method of starting anengine, comprising: substantially closing a port throttle of a cylinder;and injecting at least a portion of an amount of fuel to a cylinderduring a cylinder cycle while the port throttle is substantially closed,the amount of fuel injected being during an interval that includes amiddle position which is substantially aligned with bottom dead centerintake stroke of the cylinder. By aligning the fuel pulse with BDCintake stroke of the cylinder the possibility of fuel vaporization maybe increased.

The method includes where the amount of fuel is directly injected to thecylinder. The method also includes where the interval is a time intervalor where the interval is a crankshaft interval. In some examples, themethod includes where the engine has an air inlet throttle and where afuel comprising alcohol is injected to the cylinder during the interval.The method also includes where the amount of fuel is injected to thecylinder in two or more fuel pulses. The method further comprises atleast partially opening the port throttle after a start of fuelinjection timing.

The methods of FIGS. 7 and 9 also provides for starting an engine,comprising: substantially closing a port throttle of a cylinder during acylinder cycle; at least partially opening the port throttle during thecylinder cycle after substantially closing the port throttle and afterbeginning to inject a fuel to the cylinder during the cylinder cycle;and substantially closing the port throttle after an intake valve of thecylinder closes. The method also includes where the fuel is injectedhaving a start of injection timing that varies with alcohol content ofthe fuel. In some examples, the method includes where the fuel is portinjected.

The method may also include where the port throttle is opened at a timethat is based on a desired cylinder air amount. The method furthercomprises injecting a fuel to the cylinder during an interval during thecylinder cycle, where the interval is substantially centered aboutbottom dead center intake stroke of the cylinder. The method alsoincludes where the fuel is injected in two or more fuel pulses. Themethod further comprises advancing start of injection timing of theinterval in response to a type of fuel injected to the cylinder andwhere the interval is not substantially centered about bottom deadcenter intake stroke of the cylinder when gasoline without alcohol isinjected to the cylinder. The method also includes where at leastpartially opening the port throttle includes increasing an openingamount of the port throttle as a desired cylinder air amount increases.

As will be appreciated by one of ordinary skill in the art, the methoddescribed in FIGS. 7 and 9 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,single cylinder, I2, I3, I4, I5, V6, V8, V10, V12 and V16 enginesoperating in natural gas, gasoline, diesel, or alternative fuelconfigurations could use the present description to advantage.

The invention claimed is:
 1. A method of starting an engine, comprising:substantially closing a cylinder port throttle; and directly injectingan amount of fuel to a cylinder during a cylinder cycle while cylindervacuum varies with engine rotation and while the cylinder port throttleis substantially closed during engine cranking, the amount of fuelinjected being during an interval that includes a middle position whichis substantially aligned with a predetermined cylinder vacuum level. 2.The method of claim 1, wherein the engine is started from a stoppedposition.
 3. The method of claim 1, further comprising determining adesired amount of air based on a desired IMEP, the method furthercomprising opening the cylinder port throttle after the amount of fuelis injected.
 4. The method of claim 1, where the interval is a timeinterval or where the interval is a crankshaft interval, and where thepredetermined vacuum level substantially corresponds to a position ofbottom dead center intake stroke of the cylinder.
 5. The method of claim1, where the amount of fuel is injected to the cylinder in two or morefuel pulses.
 6. The method of claim 1, further comprising at leastpartially opening the cylinder port throttle after a start of fuelinjection timing, and where the amount of fuel is injected to thecylinder via a cylinder port.
 7. The method of claim 1, where thepredetermined cylinder vacuum level is a minimum vacuum level of thecylinder, and where the cylinder port throttle is located upstream of apoppet valve.
 8. The method of claim 7, where the engine includes an airinlet throttle and where a fuel comprising alcohol is injected to thecylinder during the interval, and where the predetermined vacuum levelis estimated via a position of the engine.
 9. A method of starting anengine, comprising: substantially closing a port throttle of a cylinderduring a cylinder cycle of engine cranking; at least partially openingthe port throttle before closing an intake valve of the cylinder duringthe cylinder cycle after substantially closing the port throttle andafter beginning to inject a fuel to the cylinder during the cylindercycle; and substantially closing the port throttle after the intakevalve of the cylinder closes.
 10. The method of claim 9, where the fuelis injected having a start of injection timing that varies with alcoholcontent of the fuel.
 11. The method of claim 9, where the fuel is portinjected; and where the port throttle is opened at a time that is basedon a desired cylinder air amount, and where air flow into the cylinderis limited via an intake valve of the cylinder closing after the portthrottle opens and before the port throttle closes.
 12. The method ofclaim 9, further comprising injecting the fuel to the cylinder within aninterval during the cylinder cycle, where the interval is substantiallycentered about a predetermined vacuum level of the cylinder as theengine rotates.
 13. The method of claim 12, where the fuel is injectedin two or more fuel pulses, and where the predetermined vacuum level issubstantially located about bottom dead center intake stroke of thecylinder.
 14. The method of claim 12, further comprising advancing startof injection timing of the interval in response to a type of fuelinjected to the cylinder, and where the interval is not substantiallycentered about bottom dead center intake stroke of the cylinder whengasoline without alcohol is injected to the cylinder.
 15. The method ofclaim 9, where at least partially opening the port throttle includesincreasing an opening amount of the port throttle as a desired cylinderair amount increases.
 16. A system for controlling an engine,comprising: an engine air intake throttle located along an engine airintake passage; a first engine cylinder port throttle located along theengine air intake passage downstream of the engine air intake throttleand upstream of a poppet valve; a first fuel injector located downstreamof the first engine cylinder port throttle and coupled to the engine todirectly inject fuel; a cylinder receiving a fuel via the first fuelinjector and air via the first engine cylinder port throttle; and acontroller including instructions for selecting a cylinder vacuum levelwhere a substantially same amount of fuel is injected to the cylinderbefore and after the cylinder vacuum level is reached during a cycle ofthe cylinder as the engine rotates, and including additionalinstructions for opening the first engine cylinder port throttle afterthe first fuel injector begins to inject fuel during the cycle of thecylinder.
 17. The system of claim 16, further comprising a second enginecylinder port throttle, and further comprising additional instructionsfor adjusting the second engine cylinder port throttle independent ofthe first engine cylinder port throttle.
 18. The system of claim 16,further comprising additional instructions for substantially fullyopening the first engine cylinder port throttle after the engine reachesa predetermined engine speed.
 19. The system of claim 16, where the sameamount of fuel injected to the cylinder before and after thepredetermined vacuum level is reached is injected in two separatepulses.
 20. The system of claim 16, further comprising additionalinstructions for substantially closing the first engine cylinder portthrottle after an intake valve of the cylinder is closed during thecycle of the cylinder.